A typical vacuum deposition source includes a mounting flange, crucible for holding deposition material, and a heating device. Both the crucible and the heating device are typically structurally supported relative to the mounting flange, which is secured to a similar flange of a vacuum chamber to position the crucible of the heating device within a desired vacuum environment. The vacuum chamber typically includes a substrate to receive deposition material from the deposition source, during use.
One commonly used heating device comprises a metal wire that is supported relative to the mounting flange in a configuration that at least partially surrounds a desired portion of the crucible. Often, a serpentine pattern is used. In use, the metal wire is heated resistively in the vacuum chamber and radiated heat from the hot wire causes deposition material provided within the crucible to form a vapor that is directed to a substrate to form a thin film of the deposition material on a surface of a substrate.
In order to resistively heat the metal wire, electrical current needs to be provided from the ambient environment, through the mounting flange, and through the metal wire. Typically, a vacuum feed-through device is used and typically includes a conductive rod surrounded by an insulating material that is sealed to a suitable vacuum flange that can be attached to the mounting flange. Such feed-through devices are well-known for passing electric current from the ambient environment outside a vacuum chamber to the vacuum environment inside the vacuum chamber.
On the vacuum side of the mounting flange, an electrical connection between the metal wire of the heating device and the conductive rod of the feed-through device needs to be made. Typically, such connection is made using conventional fasteners and connectors such as those that function by clamping the wire to the conductive post. The connection needs to remain secure during the range of temperatures that the vacuum deposition source experiences.
Alternative heating devices that can be used for vacuum deposition sources include those available from Momentive Performance Materials of Strongville, Ohio. These heating devices comprise layers of pyrolytic boron nitride and pyrolytic graphite wherein the pyrolytic graphite functions as the resistive element and is sandwiched between layers of pyrolytic boron nitride. Typically, a region of the graphite resistive element is exposed and functions as the electrical contact.
Such layered heating devices are available in various configurations including flat plates as well as cylindrical or otherwise tubular structures. In such cylindrical configurations, the electrical contacts to the resistive element comprise an arcuate surface in one configuration. In another configuration the electrical contact surface can be transitioned to a flat surface. Generally, transitioning an arcuate surface to a flat surface makes the heating device more complex and often increases cost. Moreover, transitioning an arcuate surface to a flat surface can add undesirable stress to the region of the electrical contact. Such stresses may cause undesirable cracking or delamination of the layered structure. Accordingly, for cylindrical heating devices, arcuate contacts are preferred. When used in a vacuum deposition source, the arcuate electrical contact needs to be connected to a suitable electrical feed-through device.